linux-kernel - Re: [PATCH 3/4] PCI: restrict subordinate buses to those reachable via host bridge

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Date:	Thu, 19 Jan 2012 15:13:57 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ram Pai <linuxram@...ibm.com>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	linux-pci@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] PCI: restrict subordinate buses to those reachable
 via host bridge

On Thu, Jan 19, 2012 at 1:42 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> On Wed, Jan 18, 2012 at 9:46 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>> On Wed, Jan 18, 2012 at 10:27 AM, Yinghai Lu <yinghai@...nel.org> wrote:
>>> On Wed, Jan 18, 2012 at 8:52 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>>>> If we make a quirk for this machine, we still have the question of
>>>> what to do with my patches.  I assert that if Linux ever reconfigures
>>>> any bus numbers or does any configuration of hot-added P2P bridges, it
>>>> must pay attention to the host bridge bus number window.  Therefore, I
>>>> think we need something like this series even if we make a quirk.
>>>
>>> We may need more smart way to find unused bus range instead of just
>>> just max+1 and ++max.
>>>
>>> For example:  one bridge (A) have two child bridges (B and C),
>>> A: bus range: 10-2f
>>> B: bus range: 11-1f
>>> C: bus range: 20-2f
>>>
>>> when some broken case happen, B bus BIOS assigned bus range will be
>>> all cleared in first pass.
>>> but C bus is ok.  but in second bus, bus will be assigned to 30- .
>>> that is totally wrong, We should still
>>> try to use bus 11-1f at first for bus B.
>>
>> Yes, I agree we may need a better way to choose bus numbers in the
>> first place.  My current patch (3/4) doesn't change how we choose
>> them; it only rejects invalid ones.
>
> come out draft about bus number tracking and allocate bus range instead.
>
> please check attached patch.

It's a pain to comment on attached patches vs. inline ones.

You added bus_max to pci_scan_root_bus().  I'd prefer to pass a
pointer to a struct resource, as we do for io & mem resources.  I'd
like to move away from pci_scan_root_bus() and toward a
pci_scan_host_bridge() (as in the patches I posted) that takes all the
host bridge-related info: parent, domain, resources (including bus
number range), ops, sysdata.  I don't like the current scheme of
"create it with defaults and fix them later."

The printk %pR format supports bus numbers so you don't need to print
them by hand.

struct pci_bus already has secondary & subordinate.  I don't think
adding a "struct resource busn_res" adds useful information except for
the root bus, where the bus number range comes from something external
like _CRS rather than from the upstream bridge config.

This makes pci_scan_bridge() significantly more ugly than it already
is.  I think it needs to get broken up.
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